perf bench: Improve sched-pipe.c with more comfortable output

This patch improves sched-pipe.c with more comfortable output.

Change points are comment style description and
formatting numerical values and its units.

Example:

 | % ./perf bench sched pipe
 | # Running sched/pipe benchmark...
 | # Extecuted 1000000 pipe operations between two tasks
 |
 |      Total time:5.822 [sec]
 |
 |        5.822553 usecs/op
 |          171745 ops/sec

Signed-off-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1257865442-20252-3-git-send-email-mitake@dcl.info.waseda.ac.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>